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Articles by S.P. Koh
Total Records ( 6 ) for S.P. Koh
  S.P. Koh , I.B. Aris , V.K. Ramachandaramurthy , S.M. Bashi and M.H. Marhaban
  This research presents a new approach to optimise the performance of a multiple-beam optical scanning system in terms of its marking combinations and speed, using Genetic Algorithm (GA). The problem has been decomposed into two sub problems; task segregation, where the marking tasks need to be segregated and assigned for each scanner head and path planning where the best combinatorial paths for each scanner are determined in order to minimise the total motion of marking time. The knowledge acquired by the process is interpreted and mapped into vectors, which are kept in the database and used by the system to guide its reasoning process. The main motivation for this study is to introduce and evaluate an advance new customized GA. Comparison results of different combinatorial operators and tests with different probability factors are shown. Also, proposed are the new modifications to existing crossover operator called DPPC (Dynamic Pre-Populated Crossover) together with modification of a simple crossover selection method, called BCS (Bi-Cycle Selection Method). The performance of the new operator called GA_INSP (GA Inspection Module) for a better evolutionary approach to the time-based problem has been discussed in the study. The representation approach has been implemented via a computer program in order to achieve optimized marking performance. This algorithm has been tested and implemented successfully via a dual-beam optical scanning module.
  David F.W. Yap , Y.C. Wong , S.P. Koh , S.K. Tiong and M.A.E. Mohd Tahir
  Free Space Optic (FSO) can be considered as an attractive option to fiber optic. FSO has the capability to go beyond the limit of fiber optics. Unfortunately, due to the effects of dispersion in the atmosphere, FSO, as a point-to-point communication system that requires line-of-sight transmission; suffers from attenuation and signal loss. Thus, practical and detailed research is needed to improve this wireless system. In this study, simulation on FSO propagation using measured parameter values was carried out in order to gain better understanding on the pulse behavior in free space with better level of accuracy. Using MATLAB and experimental parameter values, a more precise model can be obtained and analyzed. This will allow some level of prediction on the behavior of the propagating light pulse in the atmosphere and subsequently the FSO system performance can be further improved.
  H. Sh. Jassim , S. Yussof , S.K. Tiong , K.H. Chong and S.P. Koh
  Mobile ad-hoc network (MANET) is collection of wireless nodes that operates without using a centralized network infrastructure such as a base station. Since the wireless range is limited, the nodes mutually cooperate with their neighbors in order to extend the overall communication range of the network for forwarding packets. Ad-hoc On-demand Distance Vector (AODV) is one of the commonly used protocols in ad-hoc networks. AODV is a dynamic routing protocol that is able to find the shortest path from a source node to a destination node in MANET based on hop count. However, due to the nature of MANET, it is very easy to introduce malicious nodes in MANET. These malicious nodes may try to compromise the routing protocol functionality and make MANET vulnerable to security attacks which lead to unreliable routing. Therefore, security has become a primary concern in providing protected communication among nodes in MANET. In this study, we propose a Reliable Dynamic Trust-based Routing (RDTR) protocol by integrating a trust mechanism with a shortest path routing algorithm for establishing and maintaining trustworthy routes in MANET.
  D.F.W. Yap , S.P. Koh , S.K. Tiong and S.K. Prajindra
  Artificial Immune Systems (AIS) has generated great interest among researchers as the algorithm is able to improve local searching ability and efficiency. However, the rate of convergence for AIS in finding the global minima is rather slow as compare to other Evolutionary Algorithms. Alternatively, Genetic Algorithms (GAs) and Particle Swarm Optimization (PSO) have been used effectively in solving complicated optimization problems, but they tend to converge prematurely at the local minima. In this study, the Hybrid AIS (HAIS) is proposed by combining the good features of AIS and PSO in order to reduce this shortcoming. By comparing the optimization results of the mathematical functions and the engineering problem using GA, AIS and HAIS, it is observed that HAIS achieved better performances in terms of accuracy, convergence rate and stability.
  S.K. Tiong , David F.W. Yap and S.P. Koh
  This study proposes a novel method of introducing chaotic induced genes into Genetic Algorithms (GA) in order to solve unimodal and multimodal mathematical test functions. The integration of chaotic elements based on logistic map into GA has significantly improved the accuracy in the aspect of the best fitness value. Simulation results show that the influence of Chaos theory does improve the optimization accuracy of the mathematical functions used.
  S.K. Tiong , H.Sh. Jassim , S. Yussof , S.P. Koh and David F.W. Yap
  A mobile ad-hoc network (MANET) is a collection of mobile nodes without any specific fixed infrastructure. The connectivity among the nodes may differ with time due to nodes are randomly moving and may join or leave the network at any time. Hence, an efficient routing protocol is needed to allow communication over dynamic MANET topology. Several ad hoc routing protocols have been proposed and implemented to determine the most efficient path to route information through dynamic nodes in MANET. Meanwhile, due to most of the mobile nodes have different Quality of Service (QoS) requirements, recent research work of MANET routing has focused on developing protocol that is able to support various QoS requirements. In this study, a new routing protocol namely EMNet has been proposed to cater for different QoS requirements in MANET. It was designed based on an artificial intelligent technique namely Electromagnetic-like Mechanism (EM), which simulating the attraction-repulsion mechanism theory of electromagnetism. The EM generated solutions for new path establishment and broken links restoration by regenerating new individuals with quality improvement through its attraction-repulsion process. The new EMNet protocol has been simulated in various MANET scenarios and its performance in routing was compared with conventional ad-hoc On-demand Distance Vector (AODV) routing protocol. The simulation results show that EMNet is able to achieve better results in terms of packet delivery, normalized routing load, end-to-end delay, overhead, and throughput in comparison with AODV in the simulation scenarios.
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